Thanks for all the useful information.
Unfortunately, RGB leds did not come to my mind when designing my control panel. Would have saved me quite some space to just have one led instead of four. Probably, a standard RGB led would have been sufficient when mixing the fourth “color”, white, from the other colors using some logic.
Your information that part of the resistor network is already on the board would have been quite important when I built the Pause/Next control. I built the complete resistor network externally and wondered why the resistor values printed in the manual did not result in the expected functions. By trial-and-error, I found values that worked correctly (smaller than the recommended ones). So, I assume the pullup resistor is already on the board and by adding my own external pullup resistor I moved all the control voltage levels. Right?
I already reported the deviating resistor values to Arylic back then but they only said something about installing a new firmware. I did not try this and if it is really a “hardware problem” when the firmware probably would not fix it (unless they would change the hard-coded voltage levels in the firmware). Would also prefer a correction of the manual so that other users do not fall into the same trap as us.